The present invention relates to a damping force control type shock absorber generating a damping force against the stroke of a piston rod by controlling the flow of a fluid and capable of adjusting the damping force.
In general, a shock absorber attached to a suspension system of an automobile or other vehicle has a cylinder having a fluid sealed therein, a piston slidably fitted in the cylinder and connected with a piston rod, and a damping force generating mechanism comprising an orifice, a disk valve, etc. In response to a stroke of the piston rod, the piston slidingly moves in the cylinder, causing a flow of fluid. The flow of fluid is controlled by the damping force generating mechanism, thereby generating a damping force.
In a hydraulic shock absorber disclosed in Japanese Patent Laid-Open Publication No. 2009-281584, for example, a back-pressure chamber (pilot chamber) is formed at the back of a main disk valve constituting a damping force generating mechanism. A fluid is introduced into the back-pressure chamber to apply the pressure in the back-pressure chamber to the main disk valve in the direction for closing the valve. The pressure in the back-pressure chamber is adjusted by a solenoid valve (pilot valve), thereby controlling the valve-opening operation of the main disk valve. With this structure, it is possible to increase the degree of freedom for adjusting damping force characteristics.
Regarding the above-described damping force control type shock absorber, there is a demand for reduction in size of the solenoid valve in order to reduce power consumption, manufacturing cost, and so forth. However, a mere reduction in size of the solenoid valve limits the controllable fluid flow rate and pressure, resulting in a narrowed damping force controllable range, which makes it difficult to obtain desired damping force characteristics.